Download Chapter 9 – MUSCLE TISSUE

UNIT 5 – MUSCULAR SYSTEM
Alireza Ashraf, M.D.
Professor of Physical Medicine & Rehabilitation
Shiraz Medical school
MUSCLE TYPES
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Cardiac muscle – found only in the
heart, striated, involuntary, arranged
in figure-8 shaped bundles (for
contraction), intercalated disks
Smooth muscle – visceral (hollow
organs), non-striated, involuntary,
arranged in sheets or layers (contract
– change shape of organ)
Skeletal muscle – where muscle
connects to bone for movement,
striated, voluntary
SKELETAL MUSCLE ANATOMY
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Endomysium – delicate
connective tissue sheeth that
encloses each muscle fiber
Fasciculus – bundle of muscle
fibers covered by perimysium
(coarser fibrous membrane)
Epimysium – covers bundle of
fasciculi (entire muscle); blends
into either:
– Tendon – cord of dense,
fibrous tissue attaching a
muscle to a bone
– Aponeurosis – fibrous or
membranous sheet
connecting a muscle and the
part is moves (usually found
on torso)
MUSCLE FUNCTIONS
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Produce movement
Maintains posture
Stabilizes joints
Generates heat
MICROSCOPIC ANATOMY OF SKELETAL MUSCLE
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Sarcolemma – plasma membrane of muscle fiber (cell); under the
endomysium
Peripheral nuclei – nuclei are pushed aside by long ribbon-like organelles
called myofibrils – contain trains of tiny contractile units called sarcomeres
2 types of myofilaments in the sarcomeres:
– 1. myosin filaments – thick
– 2. actin filaments – thin
– Their arrangement produces a banding pattern, or striations
SKELETAL MUSCLE ACTIVITY
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Stimulation and contraction of single skeletal muscle cells:
– Irritability – the ability to receive and respond to a stimulus
– Contractility – the ability to shorten (forcibly) when an adequate
stimulus is received
– Nerve stimulus and action potential – one motor neuron may stimulate
a few muscle cells or hundreds of them, depending on the particular
muscle and the work it does (gross motor vs. fine motor)
 Motor unit – one neuron and all the skeletal muscle cells it
stimulates
 Neuromuscular junction – where the axon terminals for junctions
with the sarcolemma
 When the nerve impulse reaches the axon terminals, a
neurotransmitter is released, which travels across the synaptic
cleft (gap between nerve & muscle); acetylcholine (Ach) –
neurotransmitter that stimulates skeletal muscle
 Ach attaches to receptors which makes the membrane more
permeable to Na+
 Na+ diffuses in and K+ rushes out, generating an action potential
(electrical impulse), which travels over the entire surface of the
sarcolemma
 Muscle cell contracts
 ACH is removed by acetylcholinesterase to stop contraction
SKELETAL MUSCLE ACTIVITY
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steps of the action potential
Mechanism of muscle contraction: Sliding Filament Theory
– AP travels down T-tubules, which causes Ca2+ to be released from the
lateral sacs of the sarcoplasmic reticulum
– Ca2+ binds to tropinin, causing tropomyosin to move out of the way –
exposing the active site on the actin filament
– Myosin heads swing back and attach to the active site on actin,
forming cross-bridges
– Myosin heads perform a power stroke – move toward the center of the
sarcomere
– Pulling actin filaments towards the center of the sarcomere
– ATP is broken down to provide energy for the myosin heads to release
the active site; leftover energy is stored for the next power stroke
– Myosin heads grab further & further back each time
– Whole muscle shortens
– Whole series of events takes few thousands of a second
SKELETAL MUSCLE ACTIVITY
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muscle contraction video
Contraction of skeletal muscle as a whole
– Graded responses
 All-or-none law – a muscle cell will contract to its fullest extent
when it is stimulated adequately; it never partially contracts; is
true of muscle cells only (not whole muscle)
 Muscle cells react to stimuli with graded responses or different
degrees of shortening
 Can be produced 2 ways:
– 1. By changing frequency of muscle stimulation
 A single, brief, jerky contraction – muscle twitch
 Nerve impulses are delivered to the muscle at a very rapid
rate, so rapid that muscle does not get a chance to relax
completely between stimuli; as a result, the effects of the
successive contractions are “summed” (added) together
and contraction gets “stronger and smoother,” with no
evidence to relaxation seen – muscle is in fused, or
complete, tetanus, or tetanic contractions (tetanus is
normal and desirable, not to be confused with
tetanus/lockjaw, which is caused by bacterium)
SKELETAL MUSCLE ACTIVITY (CONT.)
– 2. by changing number of muscle cells being stimulated
 How forcefully a muscle contracts depends largely on the
number of muscle cells stimulated; when only a few cells
are stimulated, contractions will be slight; when all cells
are stimulated, contraction is strong
– Providing energy for muscle contraction – as muscle contracts, ATP is
broken down for energy; muscles stre a limited supply (4-6 seconds
worth), so it must be regenerated continuously. Working muscles use
3 pathways for ATP regeneration:
 1. Direct phosphorylation of ADP by creatine phosphate: a
phosphate group transfers from CP to ADP, regenerating more
ATP; CP supplies exhaust in about 20 seconds
 2. Aerobic respiration: provides 95% of ATP at rest and during
light exercise; occurs in mitochondria & involves a series of
metabolic pathways that use oxygen – called oxidative
phosphorylation; glucose is broken down into CO2 & H2O; some
released energy is captured in ATP bonds (get 36ATP/1 glucose)
 3. Anaerobic glycolysis and lactic acid formation: initial steps of
glucose breakdown occur via glycolysis which is anaerobic.
– Glucose  pyruvic acid with energy captured in ATP bonds
(2ATP/ 1 glucose)
SKELETAL MUSCLE ACTIVITY (CONT.)
– If enough oxygen is present, pyruvic acid enters aerobic
pathways that occur within mitochondria
– If there is not enough oxygen present (i.e. – intense muscle
activity), or if oxygen or glucose delivery is inadequate,
pyruvic acid is converted to lactic acid in a process called
anaerobic glycolysis
 Lactic acid - causes muscle soreness and fatigue (muscle
fatigue occurs when the muscle can no longer contract
despite still being stimulated). It results from oxygen
debt which must be “paid back” (taking deep breaths)
– Isotonic vs. isometric contraction:
 Isotonic contractions – when myofilaments are successful in
sliding movements so muscle shortens during contraction; most
familiar type (i.e. – smiling, bending at knee)
 Isometric contractions – when muscles do not shorten b/c muscles
are pitted against some more or less immovable object, but
tension keeps building (i.e. – lifting a dresser, pushing arms
against a wall)
– Muscle tone – state of continuous partial contraction
SKELETAL MUSCLE ACTIVITY (CONT.)
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Effect of Exercise on Muscles:
– Aerobic or endurance exercise
 Examples – biking, jogging, swimming laps
 Results in stronger more flexible muscles with greater resistance
to fatigue
 blood supply increases
 individual muscle cells form more mitochondria and store more
oxygen (makes overall body metabolism more efficient
 Improves digestion and elimination of wastes
 Enhances neuromuscular coordination
 Makes the skeleton stronger
 Heart enlarges
 Fat deposits are cleared from blood vessel walls
 Lungs become more efficient at gas exchange
 Does NOT cause muscles to increase in size
SKELETAL MUSCLE ACTIVITY (CONT.)
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Effects of Exercise on Muscles:
– Resistance or isometric exercise
 Examples – weightlifting, theraband or medicine ball training,
bodyweight exercises like push-ups or pull-ups, plyometrics
 Key is that muscles are being forced to contract with as much force
as possible or as quickly as possible
 Muscles increase in size and strength
– Due to enlargement of individual muscle cells (more
contractile filaments), not because more muscle fibers are
made
– Size of reinforcing connective tissue also increases to support
increased muscle size
SKELETAL MUSCLE ACTIVITY (CONT.)
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Attached Parts of a Muscle:
– Origin – part of the muscle
attached to the immovable or less
movable bone
– Insertion – part attached to the
movable bone; insertion moves
toward the origin
Types of Muscle Movement:
– Flexion – decrease angle of a joint
(hinge joints – knee & elbow)
– Extension – increases angle of a
joint (straighten knee or elbow)
– Rotation – movement of a bone
around its longitudinal axis (ball &
socket joints – shaking your head
“no”)
SKELETAL MUSCLE ACTIVITY (CONT.)
– Abduction – moving a limb
away from the midline
(raising arm or leg out to
the side)
– Adduction – moving a limb
toward the midline
(lowering arm or leg from
the side back down to the
body)
– Circumduction – proximal
end of a limb is stationary,
distal end moves in a
circle, combination of
flexion, extension,
abduction, & adduction)
– Dorsiflexion – lifting the
foot so that its superior
surface approaches the
shin
– Plantar flexion –
depressing the toes (point
the foot)
SKELETAL MUSCLE ACTIVITY (CONT.)
– Inversion – turn the sole
medially (most common
type of ankle sprain)
– Eversion – turn the sole
laterally
– Supination – forearm
rotates laterally so palm
faces anteriorly; radius &
ulna are parallel
– Pronation – forearm
rotates medially so palm
faces posteriorly; radius &
ulna form an “X”
– Opposition – movement of
thumb when touching tips
of other fingers on same
hand
INTERACTIONS OF SKELETAL MUSCLES IN THE BODY
Prime mover – muscle that has the major responsibility for causing
a particular movement
 Antagonist – muscles that oppose or reverse a movement
 Synergists – help prime movers by producing same movements
 Fixators – hold a bone still or stabilize the origin of a prime mover
so all the tension can be used to move the insertion bone (i.e. –
postural muscles that stabilize the vertebrae)
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NAMING SKELETAL MUSCLES
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Direction of the muscle fibers – usually a reference to a midline or
long axis of a limb (i.e. – rectus = straight; oblique = at a slant to)
Relative size of the muscle – maximus, minimus, longus
Location of the muscle – named for bone associated with the
muscle (i.e. – temporalis, tibialis)
Number of origins – biceps brachii, triceps brachii
Location of muscle’s origin & insertion – sternocleidomastoid
(originates on sternum & clavicle, inserts on mastoid process of
temporal bone)
Shape of the muscle – deltoid means triangular
Action of the muscle – flexor, extensor, adductor, etc.
website tutorial
ARRANGEMENT OF FASCICLES
Circular – concentric circles
around outside body opening
(sphincters – eye & mouth)
 Convergent – fascicles
converge to single tendon
(pectoralis major)
 Parallel – length of fascicle
runs parallel to long axis of
muscle
– Fusiform – spindle-shaped
muscle with expanded
belly (biceps brachii)
 Pinnate – short fascicles
attach obliquely to central
tendon (uni-, bi-, or mulit-)
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GROSS ANATOMY OF SKELETAL MUSCLES
Practical 1 – head & neck
 Facial Muscles
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Chewing Muscles
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Frontalis
Orbicularis oculi
Orbicularis oris
Buccinator
Zygomaticus
Masseter
Temporalis
Neck Muscles
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Platysma
Sternocleidomastoid
GROSS ANATOMY OF SKELETAL MUSCLES
Practical 2 – trunk muscles
 Anterior
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Pectoralis major
Intercostals (internal & external)
Muscles of the abdominal girdle:
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Rectus abdominus
External oblique
Internal oblique
Transversus abdominus
GROSS ANATOMY OF SKELETAL MUSCLES
Practical 2 – trunk muscles
 Posterior
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Trapezius
Latissimus dorsi
Erector spinae
Deltoid
GROSS ANATOMY OF SKELETAL MUSCLES
GROSS ANATOMY OF SKELETAL MUSCLES
GROSS ANATOMY OF SKELETAL MUSCLES
GROSS ANATOMY OF SKELETAL MUSCLES
GROSS ANATOMY OF SKELETAL MUSCLES
GROSS ANATOMY OF SKELETAL MUSCLES
GROSS ANATOMY OF SKELETAL MUSCLES